Neutral Amino Acids
AV P TLIMP
alanine (ala, A)
valine (val, V)
phenylalanine (phe, F)
tryptophan (trp, W)
leucine (leu, L)
isoleucine (lle, I)
methionine (met, M)
proline (pro, P)
Polar Amino Acids
STTHAGGC
serine (ser, S)
threonine (thr, T)
tyrosine (tyr, Y)
asparagine (asn, N)
glutamine (gln, Q)
glycine (gly, G)
cysteine (cys, C)
Charged Amino Acids
LAGA
lysine (lys, K)
aspartate (asp, P)
glutamate (glu, E)
arginine (arg, R)
What is the difference between pH and pKa?
pH is acidity of environment/solution
pKa is how strong the acid is does not change with concentration)
When pH = pKa, what species dominates?
50% protonated, 50% deprotonated
When pH > pKa, what species dominates?
deprotonated form/conjugated base dominates (A-)
When pH < pKa, what species dominates?
protonated form/acid dominates (AH)
What is the pKa of this?
−COOH ⇌ −COO− + H+
2
What is the pKa of this?
−NH3+ ⇌ −NH2 + H+
9.5
What is the pKa of this?
−SH ⇌ −S− + H+
9
−OH ⇌ −O− + H+
pKa varies
What is a zwitterion?
molecule that has both a positive and negative charge at the same time, but an overall net charge of zero
often exists at physiological pH (7)
What is the pl?
pl is the isoelectric point in pH at which the amino acid has no net charge
amino acid exists mostly as zwitterion
What type of molecule are amino acids>
chiral (asymmetric)
What amino acids absorbs at 280 nm?
tryptophan and tyrosine
lots of conjugation + lower energy transition + longer wavelength due to aromatic group
BUT NOT PHENYLALANINE because it lacks any substituent (only benzyl group)
